Hardware the 300 beta participants will be relatively impressive, considering they'll be receiving at their door step free of cost. Valve has no plans to make this specific hardware device available past the beta, but it gives us an indication of what SteamOS devices will be capable of.

For the GPU of the Steam Machines beta, Valve will pack some units with NVidia Titan, some GTX780, some GTX760, and some GTX660. For CPU, some boxes will have an Intel i7-4770, some i5-4570, and some i3. RAM will stay consistent across, with 16GB DDR3-1600 (CPU), 3GB GDDR5 (GPU). There'll be plenty of room of storing games thanks to a 1TB/8GB Hybrid SSHD. All of the hardware will be powered by an internal 450w 80Plus Gold - no external, bulky power supply is much appreciated for the living room.

Valve has yet to reveal a design for the Steam Machines beta, but it will be a concise 12 x 12.4 x 2.9. The prototype will be fully upgradable specification wise. It sounds like Valve wants you to tinker so they can understand the full capabilities of SteamOS, which will work on more than just Valve-official hardware.

If you don't get into the beta program and want to build your own version of the Steam Machines beta, it will be possible. "Apart from the custom enclosure, anyone can go and build exactly the same machine by shopping for components and assembling it themselves," Valve writes. "And we expect that at least a few people will do just that. (We'll also share the source CAD files for our enclosure, in case people want to replicate it as well.)"